Genetic survey finds association between CCD and virus

September 14, 2007

WASHINGTON - A team led by scientists from the U.S. Department of Agriculture's Agricultural Research Service (ARS), Pennsylvania State University (PSU), and Columbia University (CU) has found an association between colony collapse disorder (CCD) in honey bees and a honey bee virus called Israeli acute paralysis virus, according to a paper published in the journal Science this week. ARS entomologist Jeffery S. Pettis, research leader of the agency's Bee Research Laboratory in Beltsville, Md.; Diana L. Cox-Foster, a professor in the PSU Department of Entomology; and W. Ian Lipkin, director of the Center for Infection and Immunity at the Columbia University Mailman School of Public Health, led the team that did genetic screening of honey bees collected from 30 colonies with CCD and 21 colonies with no CCD from four locations in the United States. The genetic screening allowed the researchers to identify pathogens to which the sampled honey bees had been exposed. In total, the honey bees-both CCD and non-CCD honey bees-were found to harbor six symbiotic types of bacteria and eight bacterial groups, 81 fungi from four lineages, and seven viruses. The search for potential pathogens was done using a new means of sequencing the genetic material from the healthy and unhealthy bees. This technology, termed high-throughput sequencing, allows for an unbiased look at DNA from all the organisms, bacteria, fungi and viruses present in the bees. Then the DNA sequences are searched against known genomic libraries for best matches. This gives a very precise picture of the organisms present, at least to the family or genus level. Often specific species can be identified, and unknown organisms--if present--can also be catalogued for further study. The sequencing work was led by Michael Egholm, vice president of 454 Life Sciences Corp. of Branford, Conn., followed by a large group effort to further identify specific groups of microorganisms. The only pathogen found in almost all samples from honey bee colonies with CCD, but not in non-CCD colonies, was the Israeli acute paralysis virus (IAPV), a dicistrovirus that can be transmitted by the varroa mite. It was found in 96.1 percent of the CCD-bee samples. This is the first report of IAPV in the United States. IAPV was initially identified in honey bee colonies in Israel in 2002, where the honey bees exhibited unusual behavior, such as twitching wings outside the hive and a loss of worker bee populations. IAPV has not yet been formally accepted as a separate species; it is a close relative of Kashmir bee virus, which has been previously found in the United States. "This does not identify IAPV as the cause of CCD," said Pettis. "What we have found is strictly a strong correlation of the appearance of IAPV and CCD together. We have not proven a cause-and-effect connection." Even if IAPV proves to be a cause of CCD, there may also be other contributing factors-which researchers are pursuing-that stress the bee colony and allow the virus to replicate. The next step is exposing healthy hives to IAPV and seeing if CCD develops. CCD became a matter of concern in the winter of 2006-2007 when some beekeepers began reporting losses of 30 to 90 percent of their hives. While colony losses are not unexpected during winter weather, the magnitude of loss suffered by some beekeepers was highly unusual. The main symptom is finding no or a low number of adult honey bees present with no dead honey bees in the hive. Often there is still honey in the hive and immature bees (brood) are present. Pollination is a critical element in agriculture, as honey bees pollinate more than 130 crops in the United States and add $15 billion in crop value annually. There were enough honey bees to provide pollination for U.S. agriculture this year, but beekeepers could face a serious problem next year and beyond if CCD becomes more widespread and no treatment is developed. More information about CCD can be found at http://www.ars.usda.gov/is/br/ccd/.